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64 Cards in this Set
- Front
- Back
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What two pathways function during the bacterial cell cycle? |
One pathway replicates and partitions the DNA into the progeny cell and the other carries out cytokinesis. |
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What step in the development of rod-shaped cells is essential for determining cell morphology? |
The cellular location of autolysin activity and peptidoglycan support of sidewall elongation. |
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Describe peptidoglycan synthesis. |
Starts in cytoplasm when UDP is attached to NAG and some of NAM converter to NAG. After the NAM-NAG-pentapeptide block is constructed, a lipid soluble carrier named bactophenol carries it across the plasma membrne. Upon release, the units are inserted into the peptidoglycan strand. PBP enzymes known as autolysin degrade bonds in the strand so new units can be insertrd. |
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Describe binary fission. |
The cell elongated as new material is synthesized, replicates it's chromosomes, and separates newly formed DNA molecules so 1 chromosome in each half. A septum is formed mid cell and parent divided into two progeny |
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Describe cell cycle of E. Coli. |
Initiation mass is reached and replication starts at origin of replication. The replisome forms at the origin and DNA replication continues in both directions. As progeny cells are synthesized, the two newly formed origins move to opposite ends of the cell and the chromosomes following. The cell elongated as replication continues until the threshold cell length reached. Then, begins the initiation of septum formation. First, site for septum is picked and Z ring is assembled. The cell wall is assembled and thet cell divides. |
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What are halophiles? |
Microbes that require the presence of NaCl at a oncentration above 0.2 M. |
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Why do Halobacterium spp. require sodium and potassium ions? |
In order to remain hypertonic to their environment and keep plasma membrane intact and pressed firmly against cell wall |
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Define pH. |
A measure of the relative acidity of a solution; -log [H+] |
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Define acidophile. |
Microbes with growth optimum between pH 0 and 5.5 |
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Define neutrophile. |
Microbes with growth optimum between pH 5.5 and 8.0. Most bacteria and protists. |
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Define alkaliphiles. |
Microbes with growth optimum between pH 8.0 and 11.5. Most fungi and archae, photosynthetic protists |
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Describe the mechanisms microbes use to maintain an internal neutral pH. |
Exchanging potassium for protons, internal buffering, acidic tolerance response for neutrophiles. Exchanging sodium for protons in alkaliphiles and. Acidophile s transport cations in and H+ out using proton transporters. |
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Explain how extreme pH might harm microbes. |
H+ moves from high to low. Drastic changes in internal pH disrupts plasma membrane and inhibits enzymes and membrane transport proteins . Changes in external pH can alter ionization of nutrient molecules and reduce their availabilty. |
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What are cardinal temperatures? |
Minimum, optimum, and maximum |
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Why does the growth rate rise with increasing temperature and then fall again at higher temperatures? |
The rate of catalysis increases with temperature to a certain point. However, temperatures that are too high denatured enzymes, transport carriers, and other proteins. So, not only does it slow down but it will eventually stop |
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Define psychrophile. |
Microbes that grow well between 0 and 20 degrees Celsius with an optimum temperature of 15 degrees Celcius. Found in oceans, Artic, and Antarctica |
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Define psychrotroph. |
Microbes that grow well between 0 and 35 degrees Celsius. These bacteria and fungi cause refrigerated food spoilage |
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Define mesophiles. |
Microorganisms 5hwt grow in moderate temperatures, between 15 and 45 degrees Celsius with an optimum of from 25-35 degrees Celcous. Almost all human pathogens |
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Define thermophiles. |
Microorganisms that grow well between. 45 and 85 degrees Celsius. |
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Define hyperthermophiles |
Microorganisms that grow well between 85 and 113 degrees Celsius. |
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What metabolic and structural adaptations for extreme temperatures do psychrophiles and thermophiles have? |
Psychrophiles have high levels of unsaturated fatty acids in their membranes which remain semisolid when cold and use antifreezing proteins. Thermophiles have heat-stanle enzymes and protein synthesis systems that function at high temperatures. Their membrane lipids have higher melting pionts. |
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Define osmotolerant |
Ability to grow over wide ranges od water activity or osmotic concentration |
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Obligate aerobe |
Completely dependent on atmospheric oxygen to grow |
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Faculty Tiverton anaerobe |
Doesn't require oxygen but grows better in its presence |
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Aerotolerant anaerobe |
Grows equally with or without oxygen |
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Obligate anaerobe |
Does not tolerate oxygen and will die in presence |
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Microaerophile |
Requires oxygen levels between 2% and 10% for growth and damaged at atmospheric oxygen levels |
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Atmospheric oxygen level |
20% |
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What are the toxic effect od)f O2? |
Damage proteins, lipids. And nucleic acids |
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How do oxygen-tolerant microbes protect themselves from the toxic effects of O2? |
Using enzymes SOD and catalyst to catalyze the destruction of super-oxide radicalradical and hydrogen peroxide, respectively. |
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What is a biofilm? |
A group of complex, slime encased communities of bacteria |
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List two ways life in a biofilm is advantageous for microbes. |
Microbes are protected from numerous harmful agents such as UV light. The waste products of one microbe may be the energy source of another. Allows for the transfer of genes within and between species. |
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What medical challenges do biofilm present? |
Some cells are persistent cells and will survive antibiotic treatment and repopulate biofilm after treatment stops. |
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What is quorum sensing? |
Bacteria using molecular signals to communicate with each other in a density-dependent matter. The microbial cells release a certain signal molecules. When the quantity if signals reach a certain threshold, it tells the cells it okay or its time to perform a certain function. |
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Why is quorum sensing important to microorganisms? |
Some functions are most or only effective where there is a large quantity of cells. It can also be used to coordinate key activities within a population. |
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Describe defined media and it's uses. |
A medium in which all chemical components are known. Often used to culture photoautotrophs and chemoorganoheterotrophs. Used when it is desirable to know exactly what the microorganism is metabolizing. An example is BG-11 medium for cyanobacteria. |
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Oligotrophic environment |
Contains low levels of nutrients |
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Describe complex media and it's uses. |
Media that contain some ingredients of unknown chemical composition. Used when an organisms nutritional requirements are unknown or to culture fastidious organisms. Examples are nutrient broth and MAC agar |
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Describe selective media and it's uses |
Media that allows the growth of particular microorganisms but inhibits others. Ex: MAC agar, EMB agar |
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Describe supportive media and it's uses |
General purposr. Sustain growth of many organisms. Ex: nutrient broth |
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Describe enriched media and it's uses |
Supportive media plus the addition of blood and/or other nutrients to encourage growth of fastidious microbes. Ex: blood agar |
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Describe differential media and it's uses. |
Media used to distinguish between different groups of microbes and even permit tentative identification of microorganisms based on their biological characteristics. Ex: blood agar, MAC agar, Mannitol salt agar, EMB agar |
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What are peptones, yeast extract, beef extract, thioglycollate? Why are they used in media? |
Undefined components used in complex media to be sources of carbon, growth factors (vitamins, minerals, amino acids), and/or energy to the microorganisms. |
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What are pure cultures and why are they important? |
Each colony arises from a single cell. It allows for the study of one species at a time. |
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How are spread plates prepared? |
Small volume od diluted mixture containing 25 to 250 cells is transferred to center of agar plate and spread evenly over the surface with sterile bent rod. |
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How are streak plates prepared? |
Cells transferred to edge of agar plate with inoculation loop or swab and then streaked out over the surface in several pattern. Loop is sterilized after each sector and an inoculum for the rest of the sectors are obtained from the previous sections. |
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How are pour plates prepared? |
Original sample diluted several times to reduce microbial population. Small volumes of several diluted samples are mixed with liquid agar and poured into sterile culture dishes. |
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It is known that microbial growth varies within a colony. What factors might cause these variations? |
Nutrient diffusion and availability, bacterial chemotaxis, the presence of liquid in the surfacet, and the hardness of the agar |
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What is agar? Why is it used in media? |
Most commonly used solidifying agent. Melts at 90 Celcius but doesn't harden until 45 Celcius. Allows for incubation at range of temperatures. Most microorganisms can't degrade it. |
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Define microbial growth |
The growth in the size of the population |
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Describe the lag phase of microbial growth |
When microorganisms first introduced, no immediate increase on cell number. Cells are synthesizing new components and adjusting (injured and need recovery time, different medium, depleted nutrients) |
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Describe the exponential phase of microbial growth |
Growing and dividing at the maximum rate possible given genetic potential and environment. Constant growth rate and uniform population. Rate of nutrient uptake. |
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Describe the stationary phase of microbial growth |
Population growth ceashes. Number of viable organisms is constant. Balance between cell division and cell death or cells stop dividing. Nutrient limitation, acclimation of waste, reached critical population level |
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Describe the death phase of microbial growth. |
Number of viable cells decreasing at a constant rate. Dying cells-maybe be programmes or cells unable to grow |
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Why would cells that are vigorously growing when inoculated into fresh culture medium have a shorter lag phase than those that have been stored in a refrigerator? |
Adjustment for temperature change |
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Direct measurement of cell numbers |
Uses a counting chamber, membrane filter, flow cytometry, and electronic counters. Easy, inexpensive, quick. Gives info about size and morphology. However, requires large population size evenly dispersed to sample small volume. Can't distinguish between dead or alive |
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Viable counting methods |
Count only cells that are able to reproduce when cultured. Includes spread plate,pour plate, membrane filter. Simple, sensitive, and widely used. Underestimated if clumps and microorganisms not well dispersed. Hot agar in pour plate may injure or kill cells. Medium may not support growth of all viable organisms present |
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Measurement of cell mass |
Determine dry weight, spectrophotometry, based in concentration of cellular substance. Time consuming and not very sensitive |
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When using direct cell counts to follow the growth of a culture it may be difficult to tell on the culture and change the size of senescence and death. Why? |
Cells may be inactive or damaged and therfore unable to reproduce properly but not dead. Multiple stages between alive and dead based on metabolic activity, state of plasma membrane and state of cell |
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What are plate count results expressed as colony forming units? |
It is not possible to be certain that each colony arose from an individual cell |
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How would you count cells in a sample of pure culture of S. aureus? Explain. |
Like to appear in clusters so measure using cell mass. |
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How would you count the cell in a water sample that needs to be checked for E. coli contamination? Explain. |
I would use a membrane filter as a viable or direct counting method with a selective media for the bacteria. Because it is what I want to filter out as much as possible. E. Coli is common so know what looking for. Appear in singles or clusters |
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How would you count the number of cells in a sample of yogurt? Explain. |
I would use flow cytometry because there may be different bacteria or unknown bacteria. Cells may have different sizes, internal complexity, and other characteristics. The flow cytometry counts one cell at a time so it will be more accurate. |
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Describe how chemostat and turbidostat operate. How do they differ? |
Chemostat is constructed so that the rate at which a sterile medium is fed into a culture physical is the same at the rate at which the medium containing microorganisms is removed. It is a limited quantity of an essential nutrient so final cell density depends on its concentration. Rate of nutrient exchange is dilution rate. Turbidostat had a photocell that measure turbidity of the culture in the growth vessel. The flow rate of media is automatically regulated to maintain a certain level if turbidity, or cell density volume. They have different dilution rates (turbidity isn't constant) and turbidostat had all nutrients in excess. Turbidostat likes high dilution rates and chemostat likes low. |
